Workbook not opening at startup (splash screen frozen) - vba

Question

I use Excel 2016. The file I am using runs some code in workbook Open event handler.
Depending on what the code does the workbook may never get opened (visible).
in Workbook_Open the event handler establishes a connection with a data base and load some data eventually warn the user if an error occurs for instance.
Establishing the connection with a data base and load some data works most of the time. Some times it does not and the Excel splash screen remains on the screen for ever. After closing the splash screen clicking on the close cross, the Excel process continues running in the background.
If an error occurs I don't see the pop up form which is opened to warn the user as long as the workbook is not visible.
when I kill the process an reopen Excel (not the workbook), Excel suggest to retrieve the file which was opened earlier proving somehow that it has in deed been opened.
The second process just does not work unless the workbook is visible. If I run Excel and then open the workbook it s ok (in case an error occurs the warning pop up form is opened).
If Excel is closed and i open the workbook it does not work (splash screen frozen).
what is the proper way to start a VBA application where It is necessary to manage some cosmetics tasks (show some sheets, hide some other) and run a connection to a data base?
Here is a simplified version of the code (can't provide it all - too complex - too long)
In this code the function bConnectToTheDatabase is forced to return False which make the bLogin function useless (the code is not provided for this reason).
Private mLoginForm As frmLgn ' a form to login the application (see image)
Private mCustomMsgBox As frmMsgBox ' a form to display custom messages (see image)
Public Const gsPFU_VBA_PWD as String = "my secret password"
Public Const gsBLANK_WKS_NAME As String = "Blank"
Private Sub Workbook_Open()
'
Call HidShowSomeSheets()
' start the application up
Call LoginIntoTheApplication()
End Sub
' hide all sheets but the one named gsBLANK_WKS_NAME
' protect/unprotect to chnage visibility
Sub HidShowSomeSheets()
With Application.Workbooks(ThisWorkbook.Name())
.Unprotect (gsPFU_VBA_PWD)
.Sheets(gsBLANK_WKS_NAME).Visible = xlSheetVisible
For Each wks In .Sheets
With wks
.Unprotect (gsPFU_VBA_PWD)
End With
Next wks
For Each wks In .Sheets
With wks
If (StrComp(gsBLANK_WKS_NAME, .Name) <> 0) Then
.Unprotect (gsPFU_VBA_PWD)
On Error Resume Next
.Visible = xlSheetVeryHidden
Else
.Protect (gsPFU_VBA_PWD)
.Activate
End If
End With
Next wks
.Protect (gsPFU_VBA_PWD)
End With
End Sub
Sub LoginIntoTheApplication()
if( bConnectToTheDatabase() ) then
call bLogin
else
'create a custom form (it has it own even handler - block the execution flow)
'set mCustomMsgBox= new frmMsgBox
'mCustomMsgBox.Show vbModeless 'this does not work
MsgBox "something went wrong" 'this works
end if
end Sub
Function bLogin() as Boolean
'login into the application
End Function
Function bConnectToTheDatabase() as Boolean
'do the connection
'get the data
'etc ....
bConnectToTheDatabase= False 'fore it to False for the purpose of the explanation
End Function
The login form
The custom message box